The diagnosis of a variety of diseases (e.g., leukemia and AIDS) can be facilitated by studying the various sub-populations of leukocytes in the blood. Although monoclonal antibodies have been used successfully to qualitatively characterize many pathological diseases, it remains extremely difficult to quantitate monoclonal antibody binding sites on a particular cell type. Changes in the number of antibody-binding sites may serve as an index to the stage of a disease, as well as, an indicator of the effectiveness of particular medical treatments. The aim of this proposal is to develop a calibration Kit for the clinical flow cytometer that will allow an easy, direct, and inexpensive method to determine the number of monoclonal antibody binding sites per cell. The method will be based on a set of highly uniform microbeads, that behave as "model cells" in terms of both size and antibody binding behavior. These microbeads will bind specific amounts of commerically available fluorescent monoclonal mouse IgG antibodies and will serve as the standards to construct calibration plots of instrument response against the number of fluorescent antibodies using a flow cytometer. In Phase I of this project, it will be demonstrated that this calibration plot may be constructed and used to determine the number of antibody binding sites for particular cell populations. Phase II of the project will involve close collaboration with clinicians to assess the clinical applicability of this Kit, as well as, its scale-up manufacturing and commericalization. It is expected that this new technology will provide clinical and research laboratories with unique tool in the diagnosis, study, and treatment of certain disorders.